1. CS2021 Python Programming Week 3 Systems Programming PP-Part II

2. Python Documentation $open /Library/Frameworks/Python.framework/Versions/3.4/Resourc es/English.lproj/Documentation/index.html

3. Searching and Finding Documents If you cannot locate docs on local machine use web address http://www.python.org or http://www.python.org https://docs.python.org/3/ Search for docs on sys.getrecursionlimit()

4. Exploring Sys Module Run the following >>> import sys >>> dir(sys) >>> help(sys) >>>help(sys.getrecursionlimit)

5. Experiment with recursion limit >>> sys.setrecursionlimit(50) >>> sys.getrecursionlimit() =>50 >>>def countdownrec(n): if n >0: print(n) countdownrec(n-1) >>>countdown(52)

6. More.py Load PP4E/System/more.py ___________________________________________________ def more(text, numlines=15): lines = text.splitlines() # like split('\n') but no '' at end while lines: chunk = lines[:numlines] lines = lines[numlines:] for line in chunk: print(line) if lines and input('More?') not in ['y', 'Y']: break if __name__ == '__main__’: import sys # when run, not imported more(open(sys.argv[1]).read(), 10) # page contents of file on cmdline

7. 2 ways for running more.py $cd PP4E/System $python >>>from more import more >>>import sys >>>more(sys.__doc__) $cd PP4E/System $python more.py more.py

8. sys.argv #file arguments.py import sys # it's easy to print this list of course: print sys.argv # or it can be iterated via a for loop: for i in range(len(sys.argv)): if i == 0: print ("Function name: %s" % sys.argv[0]) else: print ("%d. argument: %s" % (i,sys.argv[i]))

9. Experiment with sys.argv $ python arguments.py arg1 arg2 ['arguments.py', 'arg1', 'arg2'] Function name: arguments.py 1. argument: arg1 2. argument: arg2 $

10. PP4E/System/testargv2.py "collect command-line options in a dictionary" def getopts(argv): opts = {} while argv: if argv[0][0] == '-': # find "-name value" pairs opts[argv[0]] = argv[1] # dict key is "-name" arg argv = argv[2:] else: argv = argv[1:] return opts if __name__ == '__main__': from sys import argv # example client code myargs = getopts(argv) if '-i' in myargs: print(myargs['-i']) print(myargs) $C:\...\PP2E\System>python testargv2.py {} $C:\...\PP2E\System>python testargv2.py -i data.txt -o results.txt {'-o': 'results.txt', '-i': 'data.txt'}

11. CWD and Import Paths #whereami.py import os, sys print('my os.getcwd =>', os.getcwd()) print('my sys.path =>', sys.path[:6]) # shows first 6 import paths input() Testing whereami.py $cd PP4E/System $python whereami.py $cd.. $python System/whereami.py $cd System/temp $python../whereami.py

12. Directory Tools (PP pg 163) A common system task is to process a set of files in a directory (a folder) Three ways to scan a directory – os.popen(‘ls’) – os.listdir(‘.’) – glob.glob(‘*’) >>> os.chdir('/Users/fredannexstein/Google Drive/PP4E') >>> os.popen('ls').readlines() ['Ai\n', 'Dbase\n', 'Dstruct\n', 'Gui\n', 'Integrate\n', 'Internet\n', 'Lang\n', 'LaunchBrowser.pyw\n', 'Launch_PyDemos.pyw\n', 'Launch_PyGadgets_bar.pyw\n', 'Launcher.py\n', 'Preview\n', 'PyDemos-pil-note.txt\n',…..

13. >>> os.listdir(‘.’) ['.DS_Store', '__init__.py', '__init__.pyc', '__pycache__', '_pymailerrlog.txt', 'Ai', 'Dbase', 'Dstruct', 'echo.py', 'Gui', 'Integrate', 'Internet', 'Lang', 'Launch_PyDemos.pyw', 'Launch_PyGadgets_bar.pyw', 'LaunchBrowser.pyw', 'Launcher.py', 'launchmodes.py', 'Preview', 'PyDemos-pil-note.txt', 'PyDemos.pyw', 'PyGadgets.py', 'PyGadgets_bar.pyw', 'README-PP4E.txt', 'System', 'TempParts', 'textConfig.py', 'Tools'] >>> import glob >>> glob.glob('*') ['__init__.py', '__init__.pyc', '__pycache__', '_pymailerrlog.txt', 'Ai', 'Dbase', 'Dstruct', 'echo.py', 'Gui', 'Integrate', 'Internet', 'Lang', 'Launch_PyDemos.pyw', 'Launch_PyGadgets_bar.pyw', 'LaunchBrowser.pyw', 'Launcher.py', 'launchmodes.py', 'Preview', 'PyDemos-pil-note.txt', 'PyDemos.pyw', 'PyGadgets.py', 'PyGadgets_bar.pyw', 'README-PP4E.txt', 'System', 'TempParts', 'textConfig.py', 'Tools']

14. glob Glob uses usual filename syntax of many shells for matching: ? –single char, * -any pattern, []- set of chars >>> for path in glob.glob(‘*.py'):... print(path) __init__.py echo.py Launcher.py launchmodes.py PyGadgets.py textConfig.py >>> for path in glob.glob('./*/*.py'):... print(path)./Ai/__init__.py./Dbase/__init__.py./Dbase/castdump.py./Dbase/castinit.py./Dbase/filepickle.py./Dbase/person-start.py./Dbase/person.py./Dbase/testdata.py./Dstruct/__init__.py./Gui/__init__.py./Integrate/__init__.py

15. Walking Directory Trees Application :Find all files with a global variable name os.walk yields a sequence of 3-tuples – Current directory – All subdirectories – All files within current directory – Recursively walks subdirectories import os for (dirname,subdirs,files) in os.walk ('/Users/fredannexstein/Google Drive/PP4E'): print ('[' + dirname +']') for f in files: print(os.path.join(dirname,f))

16. Exercise Using the str.endswith() function, write a python script that counts and prints all python files (ending with.py) in PP4E that reference name ‘tkinter’. You may run into the error: UnicodeDecodeError: 'ascii' codec can't decode byte 0xef in position 0: ordinal not in range(128) We will see later how to process such files, for now you will pass over errors by adding try-except handler try: if 'tkinter' in open(pname).read(): print(pname) count = count +1 except: pass